This invention relates to zippered bags, and more particularly, gusset bags and flat bags each provided with a zipper element for opening or closing an end opening of the bag through which a content filling in the bag can be easily taken out, and also is concerned with methods of forming such zippered bags.
In the known art, there has been provided a flat bag container having opposing flat portions, and four side peripheries of such bag are heat sealed (four side seal bag), and an opening of the bag through which an inner content can be taken out is closed or opened by providing a zipper element. With such a flat bag, it is possible to manufacture the bag by making coincident the delivery direction of a film material forming a flat bag container with a supply direction of the zipper element, thus being advantageous in a productivity.
Further, recently, it is attempted to apply the zipper element to a bag other than the four side seal bag, and in such attempt, a cap shaped bag member provided with a zipper element is preliminarily prepared and the cap shaped bag member is then applied to a bag body prepared separately from the cap shaped bag member. For example, a gusset bag provided with gores at both side portions of the bag body has a good self supporting property and a relatively large inner capacity, and accordingly, the usage thereof is widened and the application of the zipper element to the gusset bag has been desired.
However, since the gusset bag has a folded portion as gusset, there provided problems of difficult attachment of the zipper element.
Regarding bags other than the four side seal bag mentioned above, there is provided a bag which is generally formed of one sheet material and hence has a bonded edge like portion. Such prior art bag is shown in FIG. 29, as one example, in which, particularly, a central, i.e. back, bonded portion 952 is formed as a stepped portion providing no smooth surface portion. For this reason, it is difficult to surely apply such bag a cap shaped bag member, which is formed separately, provided with the zipper portion 965.